This article details a method for studying cardiac electrophysiology using a heart perfusion apparatus. The protocol includes electrical stimulation to assess heart rhythm and susceptibility to arrhythmias.
Take a heart perfusion apparatus connected to a data acquisition system.
Position a multi-electrode catheter for both electrical stimulation and heart rhythm monitoring.
Take a mouse heart with a cannula inserted into the aorta and connect it to the apparatus.
Perfuse the heart with an oxygenated perfusion buffer to mimic physiological circulation.
Insert the catheter into the right atrium and ventricle.
The cardiac conduction system, comprising pacemaker cells and conduction fibers, coordinates the synchronized contraction of heart chambers.
Apply electrical stimulation through the catheter to stabilize the heart's electrophysiological conditions.
Close the chamber to maintain a stable temperature.
Apply a controlled stimulation to measure baseline cardiac activity.
Next, increase the stimulation frequency to override the heart's normal rhythm, triggering irregular rhythms originating in the ventricles, known as ventricular arrhythmia.
Post-stimulation, the heart's return to a normal rhythm suggests resistance to arrhythmia, while continued abnormal rhythms indicate susceptibility.
Begin by starting the water bath, and placing the perfusion solution, including a mixture of 95% oxygen, 5% carbon dioxide in it. Then adjust the pump rate before attaching the heart so that no air bubbles are left in the cannula when mounting it to the apparatus. Set the targeted perfusion pressure to 80 millimeters mercury in the general settings and start recording.
Use an electrophysiology catheter with platinum electrodes, and electrode surface of 0.5 by 0.5 millimeters, with an electrode spacing of 0.5 millimeters for the data recording and stimulation with a designated digital stimulus generator. Then, place the catheter close to the area where the heart will be positioned after the attachment to the apparatus. Next, attach the cannula quickly to the Langendorff apparatus, and ensure that there are no bubbles left in the cannula. Switch the perfusion pressure to 80 millimeters mercury, allowing a constant pressure perfusion.
Insert the catheter carefully into the right atrium and right ventricle without touching or damaging the heart, and attach the catheter to the cannula with tape. Then, start the stimulation with the prepared cycle length of 100 milliseconds for an initial 20-minute equilibration period. Finally, close the chamber to allow a stable temperature.
Begin by applying a programmed stimulation via the distal or proximal electrodes of the catheter at twice the atrial or ventricular pacing threshold to evaluate the electrophysiological parameters. Then, perform a programmed extra stimulation or burst pacing protocols in line with the lambeth conventions to evaluate the ventricular arrhythmia genesis.
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